We have investigated the diffusion kinetics of Hf in TiN/HfSiO gate stacks. The Hf upward diffusion is found to be independent of interfacial SiO 2 growth, but depends on the amount of oxygen in the gate stacks. It is also revealed that Hf diffusion into TiN electrode occurs at above 650 C and leads to high-k degradation.

We investigated the formation of Si barrier layer by an in-situ oxygen treatment process of TiN electrode surface before poly-Si deposition. The Si depth profile after post deposition annealing (PDA) showed that no Si diffused into oxidized stacks due to the formation of TiON layers as a Si-diffusion barrier. Moreover, a high effective work function (EWF) of 4.94 eV was obtained from the oxidized stack even after PDA at 1000oC. However, we observed significant growth of interfacial SiO2 after high temperature annealing. These results indicate a trade-off relationship between EWF control and equivalent oxide thickness (EOT) scaling, and imply that an additional method for EWF modulation is required for scaled high-k devices.

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